1. Field of the Invention
This invention relates to the field of mortise locks having controllable stop means for altering operating characteristics of a handle on at least one side of the door, and in particular to a double cylinder mortise lock for commercial entrances, having means for restricted capability for changing the stop means.
2. Description of the Prior Art
Mortise locks are a well-known and popular means for affixing a closed, hinged door temporarily to its doorframe and thereby to prevent unauthorized passage through the door. A lock casing is mounted in a mortise cut into the edge of the door. A resiliently mounted latchbolt, which is biased to extend from the edge into the doorframe and may be retracted using a handle on a least one side (e.g., the indoor side) of the door, temporarily holds the door in the doorframe. The door is frequently spring-biased to close. The latchbolt has an inclined surface and bears against a strike plate such that upon closing the door the extending latchbolt is forced to retract by the edge of the strike plate, then as the door closes further the latchbolt extends into an opening in the strike plate on the doorframe.
For a more secure attachment of the door in the doorframe, a deadbolt is included in addition to the latchbolt, the deadbolt having a rectangular rather than sloping configuration and the deadbolt remaining fixed in either the extended or retracted position when so placed using a key or a control knob. The deadbolt is configured to resist retraction by use of tools forced between the door and the frame.
According to a popular style of mortise lock, the indoor-side handle and the outdoor-side handle are mounted on relatively-rotatable lengths of a spindle shaft, which are aligned axially. The handles are therefore independently rotatable, whereby one or both spindles are connected to press an eccentric projection against the spring-biased latchbolt to retract the latchbolt. Cooperating with a movable stop means, the dual-spindles are disposed at one of a range of more or less secure operating characteristics for the opposite sides of the door. For example, it may be advisable to assume a low-security operating characteristic in which a door is only temporarily latched and the knobs, levers or like handles on both the indoor and outdoor sides can be operated freely to withdraw the latchbolt. At slightly higher security but still with the deadbolt retracted, it may be advisable to prevent operation of the latchbolt at the outdoor-side handle, but to permit operation of the latchbolt from outdoors using a key. Such a change in operating characteristics is frequently accomplished using movable stop buttons.
The deadbolt is normally extended only when the door is closed. Even when a lock is in its highest security mode with the deadbolt extended, it is still advisable to permit escape from the building from inside, preferably without the need for a key. Accordingly, various means are known to disable lock functions in emergencies.
Many mortise locks have stop buttons that determine whether the handle on one side (e.g., outdoors) can withdraw the latchbolt or whether a key is needed. The usual form for movable stop buttons for setting the lock to a desired security state is a pair of buttons mounted at an edge of the door that is covered by the doorframe when the door is closed. The stop buttons are pivotally connected to flip-flop such that when one is advanced the other is automatically retracted, and vice-versa. One of the two stop buttons can then be attached to a stop abutment movable into rigid engagement to block rotation of a latchbolt-retracting part, such as the hub to which one of the handle spindles is mounted, preventing rotation of the spindle and attached handle when the stop is set. Therefore, when the stop is set and the abutment is moved to engage the hub on one side of the door, the handle on that side cannot be used to retract the latchbolt.
When a handle on one side is disabled using the stop, the door can normally still be opened on that side using a key. Mortise locks of this type may be provided with lock cylinders on one or both sides that by one means or another allow different operations to be accomplished only using different keys. Multiple levels of mastering are possible, with keys at higher levels capable of more of the operations. For example a so-called "hotel cylinder" is equipped to allow the holder of a master key to operate both the deadbolt and latchbolt, while the holder of a maid's key can operate the latchbolt only. Therefore, in the event the deadbolt is set, the maid's key will be ineffective to gain access. Hotel cylinder mechanisms according to such a description may operate by restricting the angular displacement that one key or another will cause in the lock cylinder. There are also known hotel cylinder mechanisms in which the low-level security keys will turn the cylinder in only one direction, and the high-level master keys will turn the cylinder in either direction. In the latter type of lock, turning the cylinder in one direction can be made to operate the latchbolt and turning the cylinder in the other direction can operate the deadbolt.
A mortise lock of the type that if used with a hotel cylinder is adapted to operate the latchbolt by turning the key cylinder in one direction and to operate the deadbolt by turning the key cylinder in the opposite direction is shown in U.S. Pat. No. 4,453,753--Fayerman et al (see FIG. 9 thereof), the disclosure of which is hereby incorporated. The patent also shows a lock with movable stop buttons adapted to block rotation of one of the handles when the stop is set. In that device, as a means of improving the security of the lock when the deadbolt is extended, a linkage is provided between the deadbolt and a stop button such that extension of the deadbolt automatically moves the stop button having the hub-blocking abutment into engagement with the spindle hub. In this manner, whenever the deadbolt is extended, the spindle on the relatively more restricted-access side of the door (e.g., outside) is blocked against rotation. This more positively locks the door. The stop remains set until manually released.
According to the conventional mortise lock, anyone on the indoor side and anyone with a key on the outdoor side can always open the door in the normal way, change the state of the edge-mounted stop buttons, and thereby disable the outside locking function by retracting the stops. When door is closed and locked, an intruder can sometimes insert a tool between the door and doorframe of known locks and operate the stop buttons to gain entry via the outdoor-side handle, even without bothering the latchbolt and/or deadbolt directly. An accomplice or the intruder himself can surreptitiously retract the stop buttons when the door is opened for some innocent purpose, the intruder thereafter returning to gain access because the released stops make the latchbolt retractable via the handle.
According to the prior art, the foregoing security drawbacks must be borne if the user requires the ability to change between functioning characteristics of the lock by means of stops. According to the invention, however, the stop buttons are still as useful and versatile for their security attributes as ever to persons holding a key, or possibly a master key. Nevertheless, even when the door is opened and the stop buttons exposed, the stops are blocked against any change in security characteristics by persons having no key or low security keys or persons who may by hook or by crook gain access to the edge of the door at which the stop buttons are located. The blockage of the stop buttons in the invention is physically linked with the deadbolt, which can preferably be extended only using a key or master key. A detent position of the deadbolt between full extension and full retraction of the deadbolt is provided at which the stop buttons can be re-positioned when the deadbolt is extended or retracted using a key. The stop buttons cannot be re-positioned when the deadbolt is fully either extended or retracted. The deadbolt is biased towards full extension and/or full retraction. Retraction of the deadbolt using the indoor-side handle (e.g., during emergency escape) bypasses the detent position. Placing the deadbolt at the detent requires a key; therefore, the position of the stop buttons is secure.